import heapq as h
N,M=map(int,input().split())
H=list(map(int,input().split()))
G=[[]for _ in range(N)]
for _ in range(M):
 a,b=map(int,input().split())
 a-=1
 b-=1
 G[a].append(b)
 G[b].append(a)
d=[[-1]*2 for _ in range(N)]
d[0][0]=0
q=[(0,0,0)]
while q:
 e,v,f=h.heappop(q);e=-e
 for n in G[v]:
  if H[n]>H[v]:
   if f==0 and d[n][0]<e+1:
    d[n][0]=e+1
    h.heappush(q,(-(e+1),n,0))
  else:
   if d[n][1]<e+1:
    d[n][1]=e+1
    h.heappush(q,(-(e+1),n,1))
a=max(d[-1])
print(a+1 if a>=0 else a)